Rare earth elements as nonabsorbable fecal markers in studies of iron absorption

Fecal Iron Measurement in Studies of the Human Intestinal Microbiome

Iron is an essential micronutrient for humans and their intestinal microbiota. Host intestinal cells and iron-dependent bacteria compete for intraluminal iron, so the composition and functions of the gut microbiota may influence iron availability. Studies of the effects of the microbiota or probiotic interventions on host iron absorption may be particularly relevant to settings with high burdens of iron deficiency and gastrointestinal infections, since inflammation reduces iron bioavailability and unabsorbed intraluminal iron may modify the composition of the microbiota. The quantification of stool iron content may serve as an indicator of the amount of intraluminal iron to which the intestinal microbiota is exposed, which is particularly relevant for studies of the effect of iron on the intestinal microbiome, where fecal samples collected for purposes of microbiome characterization can be leveraged for stool iron analysis. However, few studies are available to guide researchers in the selection and implementation of stool iron assays, particularly because cross-comparison of available methods is limited in literature. This review aims to describe the available stool iron quantification methods and highlight their potential application in studies of iron-microbiome relationships, with a focus on pediatric research. MS-based methods offer high sensitivity and precision, but the need for expensive equipment and the high per-sample and maintenance costs may limit their widespread use. Conversely, colorimetric assays offer lower cost, ease of use, and rapid turnaround times but have thus far been optimized primarily for blood-derived matrices rather than stool. Further research efforts are needed to validate and standardize methods for stool iron assessment and to determine if the incorporation of such analyses in human microbiome studies 1) yields insights into the interactions between intestinal microbiota and iron and 2) contributes to the development of interventions that mitigate iron deficiency and promote a healthy microbiome.

ICRP Publication 141: Occupational Intakes of Radionuclides: Part 4

The 2007 Recommendations (ICRP, 2007) introduced changes that affect the calculation of effective dose, and implied a revision of the dose coefficients for internal exposure, published previously in the Publication 30 series (ICRP, 1979a,b, 1980a, 1981, 1988) and Publication 68 (ICRP, 1994b). In addition, new data are now available that support an update of the radionuclide-specific information given in Publications 54 and 78 (ICRP, 1989a, 1997) for the design of monitoring programmes and retrospective assessment of occupational internal doses. Provision of new biokinetic models, dose coefficients, monitoring methods, and bioassay data was performed by Committee 2 and its task groups. A new series, the Occupational Intakes of Radionuclides (OIR) series, will replace the Publication 30 series and Publications 54, 68, and 78. OIR Part 1 (ICRP, 2015) describes the assessment of internal occupational exposure to radionuclides, biokinetic and dosimetric models, methods of individual and workplace monitoring, and general aspects of retrospective dose assessment. OIR Part 2 (ICRP, 2016), OIR Part 3 (ICRP, 2017), this current publication, and the final publication in the OIR series (OIR Part 5) provide data on individual elements and their radioisotopes, including information on chemical forms encountered in the workplace; a list of principal radioisotopes and their physical half-lives and decay modes; the parameter values of the reference biokinetic models; and data on monitoring techniques for the radioisotopes most commonly encountered in workplaces. Reviews of data on inhalation, ingestion, and systemic biokinetics are also provided for most of the elements. Dosimetric data provided in the printed publications of the OIR series include tables of committed effective dose per intake (Sv per Bq intake) for inhalation and ingestion, tables of committed effective dose per content (Sv per Bq measurement) for inhalation, and graphs of retention and excretion data per Bq intake for inhalation. These data are provided for all absorption types and for the most common isotope(s) of each element. The online electronic files that accompany the OIR series of publications contains a comprehensive set of committed effective and equivalent dose coefficients, committed effective dose per content functions, and reference bioassay functions. Data are provided for inhalation, ingestion, and direct input to blood. This fourth publication in the OIR series provides the above data for the following elements: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), actinium (Ac), protactinium (Pa), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), and fermium (Fm).

Rectal effluent as a research tool

Studies of localized secretions are generally superior to those of blood because they contain higher concentrations of molecules specific to the organ of interest. A common method used to analyze localized secretions is lavage. The flow of fluid over the lining of a cavity picks up both cells and soluble factors, and the effluent can be collected for study. Gastrointestinal (GI) lavage is easily and noninvasively performed by the administration of gut lavage solutions such as those routinely given to patients prior to colonoscopy, with GI lavage fluid being the copious, watery rectal effluent subsequently induced. Residual effluent is currently suctioned from the colon and discarded during colonoscopy. With millions of routine colonoscopies performed per year, GI lavage fluid is a rich and largely untapped resource for basic and clinical research. Rectal effluent can also be easily collected in a toilet receptacle without need for a colonoscopy. Rectal effluent generated in this manner has been used to study diarrheal disease, mucosal immunology, inflammatory bowel disease, celiac disease, and cancer. It is often referred to as gut lavage, colon lavage, GI lavage, or whole gut lavage fluid, which makes it challenging to locate previous studies in the literature and there are currently no comprehensive reviews of its use as a research tool. This review attempts to fill this void by discussing previous applications of rectal effluent in research and the methods that have been developed for its collection, stabilization, and analysis.

Effects of different complementary feeding regimens on iron status and enteric microbiota in breastfed infants

OBJECTIVE

To compare iron status in breastfed infants randomized to groups receiving complementary feeding regimens that provided iron from fortified infant cereals or meats, and to examine the development of the enteric microbiota in these groups.

STUDY DESIGN

Forty-five exclusively breastfed 5-month-old infants were randomized to 1 of 3 feeding groups (FGs)-commercially available pureed meats, iron- and zinc-fortified infant cereals, or iron-only fortified infant cereals-as the first and primary complementary food through 9-10 months of age. Dietary iron was determined by monthly 3-day diet records. Iron status was assessed at the end of the study by measurements of hemoglobin, serum ferritin, and soluble transferrin receptor levels. In a subsample of 14 infants, enteric microbiota were profiled in monthly stool samples (5-9 months) by 16S ribosomal RNA gene pyrosequencing.

RESULTS

Infants in the 2 cereal FGs had 2- to 3-fold greater daily iron intakes versus the meat FG (P < .0001). More than one-quarter (27%) of the infants had a low serum ferritin level, and 36% were mildly anemic, with no significant differences by FG; more infants in the meat FG had a high soluble transferrin receptor value (P = .03). Sequence analysis identified differences by time and FG in the abundances of several bacterial groups, including significantly more abundant butyrate-producing Clostridium group XIVa in the meat FG (P = .01) CONCLUSION: A high percentage of healthy infants who were breastfed-only were iron-deficient, and complementary feeding, including iron exposure, influenced the development of the enteric microbiota. If these findings are confirmed, then reconsideration of strategies to both meet infants' iron requirements and optimize the developing microbiome may be warranted.

Determination of protein and amino acid digestibility in foods including implications of gut microbial amino acid synthesis

To meet the protein and amino acid requirements of individuals and of populations requires information not only about their requirements but also about the capacity of available foods to meet those requirements. Most of our current knowledge of the digestibility of food proteins and the methods to estimate it has been derived from work with animals. Because the microbiota of the large intestine alter the amino acid composition of the digesta, and because only trivial quantities of amino acids are absorbed intact from the large intestine, the current method of choice for assessing amino acid digestibility is ileal digestibility corrected for basal endogenous losses, that is, standardized ileal digestibility. For protein as a whole, however, because nitrogen absorbed in forms other than as amino acids can contribute to the nitrogen economy, the absorption of nitrogen over the whole digestive tract is the more appropriate measure. Most of the methods developed for estimating ileal amino acid outflow in animals are not directly applicable to man: the exception is the use of volunteers with an ileostomy. The flow and composition of ileal digesta in human subjects can also be measured by the infusion of a marker and withdrawal of samples through a naso-intestinal tube. However, this method is too demanding for routine use and is likely to be restricted to validating the application to humans of digestibility data obtained either from animals, of which the pig seems most suitable, orin vitromethods. Microbial activity in the gastrointestinal (GI) tract is not confined to the large intestine: the numbers and metabolic activity of the upper GI microbiota lead to substantial amounts of microbial protein leaving the ileum. It appears however that a large proportion of the amino acids used by the upper GI microbiota are preformed - from the diet or from endogenous materials - rather than fromde novosynthesis. Although there are still uncertainties about the impact of microbial activity in the upper GI tract, the amino acid composition of ileal digesta provides the best available basis for estimating the proportion of dietary amino acids available for metabolism.

Comparison of urinary monitoring, faecal monitoring and erythrocyte analysis of stable isotope labels to determine magnesium absorption in human subjects

We have evaluated urinary monitoring and erythrocyte analysis to determine Mg absorption in human subjects as alternatives to the conventional technique of faecal monitoring by stable-isotope techniques. Ten healthy adults received 2·2 mmol 25Mg in water, together with wheat bread, followed 15 min later by intravenous injection of 0·6 mmol 26Mg (day 1). Brilliant blue and Yb (given on day 0 and day 1 respectively) served as qualitative and quantitative faecal markers. Urine was collected for 6 d after test meal intake. Complete collections of faeces were made until excretion of the second brilliant blue marker (given on day 7). Mg isotope ratios were determined by thermal ionisation-MS in urine and faeces and by inductively coupled plasma-MS in erythrocytes. Absorption was determined based on: (1) 6 d urine pools; (2) 24 h urine pools (collected 22–46 h after test meal intake); (3) erythrocytes from a blood sample drawn on day 14; (4) complete 6 d faecal pools; (5) faecal pools based on the first three consecutive stools after excretion of the first brilliant blue marker. Differences in mean Mg absorption (42 44 %) were statistically insignificant between techniques, except when based on 6 d urine pools for which the value was significantly lower (33 (sd 7) %, P=0·0003, ANOVA). The results indicate that Mg absorption can be determined from 24 h urine pools or erythrocytes obtained 14 d after test meal intake, an alternative method to the more time-consuming and labour-intense faecal monitoring. The choice of technique depends on practical and financial considerations.

Profiles of faecal output of rare earth elements and stable isotopic tracers of iron and zinc after oral administration

The objectives of this study were to confirm the non-absorbability and the reproducibility of faecal excretion kinetics of orally administered rare earth elements, and to investigate the excretion profiles of rare earth elements and stable isotopic tracers of Fe and Zn to establish the extent to which rare earth element markers duplicate the behaviour of isotopic tracers. Two investigations were performed: (1) six healthy subjects consumed a solution containing five rare earth elements in amounts varying from 1 to 10 mg; (2) seven healthy subjects were given a standard solution labelled with Sm marker and57Fe tracer, and a meal labelled with Yb marker and58Fe and70Zn tracers. Individual faecal samples were collected and analysed to determine recoveries of rare earth elements and unabsorbed isotopic tracers. The mean values for recoveries were 94·1 (SD 4·5) % FOR THE FIVE RARE EARTH ELEMENTS, AND 103 (sd 3·0) % and 99·8 (sd 2·8) % for Sm and Yb respectively. For Fe consumed with the solution, excretion kinetics of the rare earth element marker and unabsorbed tracers with cumulative collections of the first two and three faecal samples were identical, but endogenous excretion of Fe was significant (P<0·05) in stools collected after the third. For Fe and Zn consumed with the meal, the excretion kinetics for the first two individual faecal samples and composites of sequential outputs were identical. Rare earth elements can be used as markers in studies of measurement of absorption. The dose of tracer required for the measurement of absorption would be reduced proportionally to the reduction of the period of faecal sampling, so that studies with stable isotopes would be more economical, thus enabling epidemiological investigations.

Dietary inulin intake and age can significantly affect absorption of the faecal marker dysprosium in rats

It is believed that rare earth elements are not absorbed, and thus they are generally used in some mineral absorption studies as a faecal marker. The aim of the present study was to determine the effect of inulin intake and age on dysprosium (Dy) absorption in rats. Eighty male Wistar rats of four different ages (2, 5, 10 and 20 months) were randomised into either a control group or a group receiving 3·75% inulin in their diet for 4d and then 7·5% inulin until the end of the study. The animals were fed fresh food and waterad libitumfor 30d. The intestinal absorption of Dy was determined from a 4d (day 21 to day 25) balance study. Mean faecal Dy recovery (%) in the eight groups (3 months control, 3 months inulin, 6 months control, 6 months inulin, 11 months control, 11 months inulin, 21 months control, 21 months inulin) was 94·0 (sd 8·6), 64·8 (sd 10·1), 95·8 (sd 9·4), 81·5 (sd 12·1), 98·4 (sd 9·8), 87·8 (sd 9·5), 97·8 (sd 6·2) and 84·9 (sd 10·9), respectively. Our results showed clearly that dietary inulin intake decreased faecal Dy recovery in all four rat groups, and faecal Dy recovery was significantly higher in the old rats (10 and 20 months) than in the young and adult rats. These results show that the faecal recovery (or intestinal absorption) of Dy may vary greatly with nutritional or physiological states such as inulin intake or age. The use of rare earth elements as a faecal marker should be thus validated under each nutritional or physiological state before being employed in mineral absorption studies.

Dysprosium as a nonabsorbable fecal marker in studies of zinc homeostasis

BACKGROUND

Dysprosium is a nonabsorbable rare earth element that has had successful application as a marker for fecal excretion of unabsorbed zinc.

OBJECTIVE

Our goals were 1) to evaluate the efficacy of administering dysprosium with all meals over several days as a method of determining the completeness of fecal collections, 2) to determine the similarity of gastrointestinal transit kinetics and excretion patterns of dysprosium and zinc tracer administered simultaneously over several days, and 3) to evaluate alternative methods of using the data for fecal excretion of orally administered zinc tracer and dysprosium to measure the fractional absorption of zinc.

DESIGN

70Zn and dysprosium were administered orally with all meals for 5 consecutive days to 7 healthy, free-living adults consuming a constant diet based on habitual intake. Additional tracers, 67Zn and 68Zn, were administered intravenously. Urine and fecal samples were collected during tracer administration and for 8 d after the last dose. Isotope ratios were measured in urine and feces, and total zinc and dysprosium were measured in fecal samples.

RESULTS

The mean recovery of dysprosium was 101.3 +/- 2.4%. The zinc oral tracer and dysprosium had similar fecal excretory patterns; the correlation coefficient for 70Zn and dysprosium in fecal samples exceeded 0.99 (P < 0.0001) for each subject. Fractional zinc absorption measurements using various dysprosium methods correlated well (r > 0.95) with those from the fecal monitoring and dual-isotope-tracer ratio methods.

CONCLUSION

Administration of dysprosium is a useful means of determining the completeness of fecal collections and of measuring zinc absorption.

Dysprosium chloride as a nonabsorbable gastrointestinal marker for studies of stable isotope-labeled triglyceride excretion in man

OBJECTIVE

The aim of this work was to determine if dysprosium chloride (DyCl(3)) is a suitable nonabsorbable marker for studies of labeled-triglyceride excretion in cystic fibrosis patients allowing excretion to be determined accurately after analysis of one or two stools.

METHODS

A series of 66 absorption studies were conducted in 36 young cystic fibrosis patients over a five year period. All tests consisted of ingesting a single test meal containing both (13)C-labeled triglyceride (TG*) and DyCl(3); in most studies the food colorant brilliant blue (FD&C blue #1) was administered along with the DyCl(3). Ingestion of the test meal was followed by collection of individual stools for 72 to 96 hours. Stools were analyzed for (13)C-Excess ((13)C*) and Dy.

RESULTS

Excretion of Dy in cystic fibrosis patients who exhibited a wide-range of steatorrhea was quantitative. Fractional excretion of Dy and (13)C* in individual stools showed a high linear correlation (r(2) = 0.969) with a slope and y-intercept close to unity and zero, respectively. As a result, estimates of TG* excretion based on analysis of only two stools (partial pool method, PPM) were not different from those based on the analysis of all stools or stool composites. This was true both when Dy content and when stool color due to ingested brilliant blue was used to determine which stools to analyze for the PPM.

CONCLUSIONS

Combining the use of Dy and brilliant blue permits reasonably accurate estimates of fecal TG* excretion after analysis of samples from two easily identified stools. This practical method can be used to address many important clinical and experimental questions regarding triglyceride digestion and absorption that may otherwise go unanswered.

Measurement of magnesium absorption and retention in type 2 diabetic patients with the use of stable isotopes

BACKGROUND

Magnesium deficiency has been associated with type 2 diabetes and may reduce insulin sensitivity and impair glucose tolerance. The etiology of magnesium depletion in diabetes is unclear. Animal studies suggest that diabetes may impair magnesium absorption; however, there are no published data on magnesium absorption in humans with diabetes.

OBJECTIVE

Magnesium absorption from a test meal and the excretion and retention of magnesium were compared between patients with type 2 diabetes and healthy control subjects.

DESIGN

A meal labeled with 10 mg (26)Mg isotopic label was administered, and stool and urine samples were collected for 10 and 6 d, respectively. Apparent absorption was calculated as the difference between the oral dose of (26)Mg isotopic label and the total amount of the isotopic label excreted in the feces. Magnesium retention was calculated from the apparent absorption and urinary excretion of (26)Mg isotopic label in the 6 d after administration.

RESULTS

Mean (+/- SD) values for fractional magnesium absorption in the diabetic patients and the control subjects were 59.3 +/- 7.0% and 57.6 +/- 8.5%, respectively (NS). Mean (+/- SD) urinary magnesium excretion values in the diabetic patients and the control subjects were 11.2 +/- 2.6% and 11.7 +/- 3.8%, respectively (NS); retention values were 54.2 +/- 7.1% and 51.4 +/- 6.1%, respectively (NS).

CONCLUSION

Dietary magnesium absorption and retention are not impaired in patients with reasonably well-controlled type 2 diabetes.

A novel dual radio- and stable-isotope method for measuring calcium absorption in humans: comparison with the whole-body radioisotope retention method

BACKGROUND

Dietary calcium absorption can be determined only with the use of isotope techniques. Currently used isotope techniques require exclusive equipment or are not true tracer approaches.

OBJECTIVE

The objective was to compare a dual-isotope method combining radioisotopes and stable isotopes with a whole-body radioisotope retention method for measuring calcium absorption.

DESIGN

Seven healthy adults aged 21-27 y consumed a test meal containing 63 +/- 14 (macro x +/- SD) mg Ca together with a water solution of (47)Ca (0.11 MBq). One hour after ingestion, 18 mg (44)Ca was administered intravenously. All feces and urine were collected for 5 and 6 d, respectively. Calcium absorption was estimated from whole-body retention of the radioisotope 12 times over 3 wk after ingestion and from the excretion of (47)Ca and (44)Ca in a 24-h urine sample collected on day 2. (44)Ca in urine was determined by inductively coupled plasma mass spectrometry.

RESULTS

Mean (+/- SD) calcium absorption was 75 +/- 9% with the dual-isotope method and was 74 +/- 8% with the whole-body radioisotope retention method. There was a high degree of agreement between the methods.

CONCLUSION

The dual-isotope method is a valid approach for measuring calcium absorption from a single meal.

Use of stable isotopes to assess the bioavailability of trace elements: a review

The bioavailability (utilization) of trace elements is very variable, depending on the characteristics of the element itself, composition of the diet, gastrointestinal conditions and other physiological factors. To derive dietary recommendations and make use of emerging information on diet-gene interactions relating to nutritional requirements for trace elements, methods for assessing bioavailability are required. The trace elements of particular interest include iron, zinc, selenium and copper because of problems of deficiency, purported links with chronic diseases, and the growing market in fortified foods and supplements. The absorption and subsequent metabolism of trace elements can be monitored using stable isotope tracers, but there are difficulties associated with this approach. Although radioisotopes offer many advantages over stable isotopes, their use is restricted due to safety and ethical issues. The difficulties and limitations of methodologies associated with labelling of trace elements in foods with stable isotopes, design of human studies to generate results that predict bioavailability, and detection and quantification of stable isotopes in biological samples are discussed.

A review of the MAFF Optimal Nutrition Status research programme: folate, iron and copper

OBJECTIVE

The objective was to conduct a critical appraisal of research conducted within one of the UK government's research programmes, Optimal Nutrition Status, and to place the findings of this work in the context of the international research effort, to assist policy makers and advisers. Nine nutrients are addressed within the programme; the findings for three of these are reported here: folate/folic acid, iron and copper.

DESIGN

To conduct the review, the researchers had access to all unpublished progress reports, submitted to officials, arising from the projects. The overall assessment criterion was whether the information generated by the research programme could be regarded as reliable experimental data of direct relevance to setting optimal dietary requirements for the particular micronutrients. However, findings were also assessed against specific scientific criteria concerning understanding of the bioavailability, interactions, development of functional markers and inter-individual variations in metabolism, for each of the nutrients scrutinised.

RESULTS

The results of the review indicated that many important questions are indeed being addressed by the UK government's research programme, and that the work is contributing to the overall research effort being conducted world-wide on this important subject.

CONCLUSIONS

Many major questions still need to be addressed before it will be possible to identify optimal intakes for various sub-populations. These priorities are summarised in the paper.

Iron

The most useful and appropriate methods for assessing the bioavailability of (nonheme) iron supplements are described. When the supplement can be labeled isotopically, the best method for measuring bioavailability is hemoglobin incorporation, followed by fecal monitoring. Caco-2 cell in vitro systems can be used for rapid screening to predict potential availability for absorption. If the compound cannot be labeled, then the plasma appearance/disappearance of oral iron given together with an intravenous dose of iron isotope can be used to quantify absorption. With oral doses in excess of 25 mg, the 4- to 6-h plasma concentration can provide a qualitative assessment of bioavailability. Approaches for normalizing results to minimize intraindividual and interindividual variability in efficiency of iron absorption are discussed.

Mineral-binding milk proteins and peptides; occurrence, biochemical and technological characteristics

Minerals and trace elements in cow's milk occur as inorganic ions and salts or form complexes with proteins and peptides, carbohydrates, fats and small molecules. The main mineral binder or chelators of calcium are the caseins, alphas1-casein, alphas2-casein, beta-casein and kappa-casein, but also whey proteins and lactoferrin bind specific minerals like calcium, magnesium, zinc, iron, sodium and potassium. Less documented is the binding of trace elements. Peptides obtained by in vitro or in vivo hydrolysis act as mineral trappers through specific and non-specific binding sites. They may then function as carriers, chelators, of various minerals and thus enhance or inhibit bioavailability. Peptides from milk proteins have found interesting new applications in the food industry as products with improved functionality or as ingredients of dietary products, or used in pharmaceutical industry. Fortification of foods with minerals in a low concentration has for a long time been used in some countries to overcome mineral deficiency, which is an increasing problem in humans. These types of foods are being used to create a new generation of super foods in the industry today.

Use of the stable isotope (106)Cd for studying dietary cadmium absorption in humans

Hydroponically grown wheat was intrinsically labelled with the stable isotope 106cadmium (106Cd) and the flour made into a porridge. The abundance of the isotope in the porridge was approximately 30 times the natural abundance, but the total level of Cd in the porridge was 0.03 mg/kg fresh weight, which was the same as expected in a normal diet. Cadmium measurements were made using inductively coupled plasma-mass spectrometry (ICP-MS). The porridge was eaten at breakfast by adult and infant volunteers. Bulked faecal collections were analysed for unabsorbed Cd. Initial results suggest that the apparent absorption of Cd may be higher than 5% as commonly quoted, but longer faecal collection times may be necessary to confirm this.

Short-term ingestion of chlorogenic or caffeic acids decreases zinc but not copper absorption in rats, utilization of stable isotopes and inductively-coupled plasma mass spectrometry technique

The amount of dietary trace elements absorbed from a meal depends, among other factors, on the quantities of certain minor plant constituents present in the meal. These substances can act as ligands and bind trace elements in the digestive tract in available or unavailable forms for absorption. The present study was designed to investigate the extent to which different polyphenols (PP) may influence Zn and Cu absorption in rats. Different PP of nutritional interest (chlorogenic acid, caffeic acid, catechin and rutin) were studied using meals extrinsically-labelled with stable isotopes 67Zn and 65Cu. Male Wistar rats were fed on a non-labelled semi-synthetic diet containing (mg/kg) 38 Fe, 35 Zn and 7.5 Cu for 8 d. PP were dissolved in dimethyl sulfoxide as the solvent and added to the meal at 1 g/kg during 3 d before isotope administration and until the end of the experiment (a further 3 d). The control group received the dimethyl sulfoxide only. After overnight food deprivation, rats were fed on the labelled test meals (4 g diet +0.1 mg 67Zn and 0.1 mg 65Cu) with 0.5 mg Dy as a faecal marker. Faeces and urine pools were collected for 3 d and analysed for 67Zn and 65Cu isotopic enrichment using the inductively-coupled plasma mass spectrometry technique. Zn absorption was significantly less in rats fed on chlorogenic acid or caffeic acid than in the control group. Catechin ingestion non-significantly inhibited 67Zn absorption. However, the PP studied were without effect on Cu absorption. The study illustrates the effect of metal-binding phenolic compounds on mineral nutrition in the rat, and the possible importance of the effects of different foods rich in these compounds on mineral absorption in man.